MC reservoir sight glass leak

[Skinner]

So I learned a lesson this weekend. While cleaning out the garage I found a large puddle on the floor under the bike. Clear liquid, not much odor, but it was slippery: brake fluid. Further investigation showed fluid had dripped on several painted parts so I freaked out a bit, then proceeded to clean the fluid off of everything. It was then that I noticed the master cylinder reservoir sight glass was raised on one side and the reservoir was empty.

Over the winter I replaced the old, cracked, cloudy sight glass with a watch crystal. I originally used silicone, then epoxy, to hold it in place, but these things didn't hold up well to brake fluid. So I tried again, this time with JB Weld. I set the glass in place then sealed around the edges with the JB. All was well - no leaks and it looked good. I installed it and that was that. Until yesterday. Apparently the JB Weld did not have a good enough grip on the edge of the glass - it was slightly convex so I thought the JB would hold it. Well, it didn't and the glass came loose on one side, allowing the fluid to drain from the reservoir.

So I decided that I was done screwing around with this and I filled the sight glass space completely with JB weld and painted it black. I'll just have to check the fluid level manually on occasion, but I won't have to worry about any more leaks. For those that are unaware, the front reservoir sight glass on the Katana is an oddball size, around 21mm, not the 18mm that almost every other sight glass is. I could not find a replacement anywhere, so the watch crystal seemed the way to go. It's a moot point now.

On a side note - I was looking on EBay at a front MC for an early model Hayabusa. The angle of the reservoir is the same as or close to that on the Katana. The only thing I'm concerned about is the lack of a mirror perch. The Katana has one on the MC handlebar clamp, the Hayabusa does not. The clamp piece from the Katana may or may not fit the Busa so I didn't want to go down that road just for the sake of a sight glass. And it's almost impossible to find a front MC for a 1982 Katana. And they're no longer available OEM.

[Nessism]

I think you are playing with fire. I'd replace the master ASAP.

This style master has an angled reservoir and should work. It has a mirror lug too. https://www.ebay.com/itm/08-2008-KAW...kAAOSw-mda-3FO

[Skinner]

I think you are playing with fire. I'd replace the master ASAP.

Hi Ed,

I appreciate your input, but why do you think I'm playing with fire? The MC is in otherwise good condition. New piston/cup, new reservoir seal. I think the JB Weld will fill the void nicely.

[Steve]

Before you fill the void with JB, try a small piece of Plexiglass or Lexan. I have done several over the years, with no reported or observed failures.

.

[Skinner]

Before you fill the void with JB, try a small piece of Plexiglass or Lexan.

Too late.

I filled the void yesterday and painted it last night. Ready to reinstall tonight.

[Steve]

Maybe somebody else will see it in time.

.

[Skinner]

Maybe somebody else will see it in time.
.

Not sure I understand what you mean...

[fixmybrokecomputer]

Before you fill the void with JB, try a small piece of Plexiglass or Lexan. I have done several over the years, with no reported or observed failures..

I think he was saying that if someone else has the same problem, that they might see his suggestion and act on it, before they remove the sight glass and fill the hole with JB weld. I would say that the issue that one might have with your choice of repair would be that the JB will blow out with possible catastrophic results. A prudent person that didn't have a death wish would probably take their advice. Visits to the emergency room are crazy expensive.....buy another master cylinder and pinch pennies somewhere else.
My son dropped his Concours 14 at about 5 or 10 mph in Feb. That little accident was about $50,000 so far and it's not over. Does $100 or less mean that much to you? Have a look at the pics for all the drama even a low speed drop can create.

https://photos.app.goo.gl/Q8mIFBCZOJkQPBcj1

[glib]

I think he was saying that if someone else has the same problem, that they might see his suggestion and act on it, before they remove the sight glass and fill the hole with JB weld. I would say that the issue that one might have with your choice of repair would be that the JB will blow out with possible catastrophic results. A prudent person that didn't have a death wish would probably take their advice. Visits to the emergency room are crazy expensive.....buy another master cylinder and pinch pennies somewhere else.
My son dropped his Concours 14 at about 5 or 10 mph in Feb. That little accident was about $50,000 so far and it's not over. Does $100 or less mean that much to you? Have a look at the pics for all the drama even a low speed drop can create.
https://photos.app.goo.gl/Q8mIFBCZOJkQPBcj1

That's rough. I had a buddy go down Sunday (too hot in a turn), slid across the gravel shoulder, several feet up the mountain and back down and thankfully walked away with a sprained thumb--and is probably sore as hell today. Could have been so much worse. What was your son wearing for pants? Any armor? (I'm looking for myself and my son now).

[fixmybrokecomputer]

He had on jeans and a couple of layers of thermals under that. It was 17 that morning. I'm speculating it was a combo of too much throttle, cold tires and cold street. I don't know that armor would have helped him. It was a spiral break in his tibia, so I'm just guessing that somehow his lower leg got twisted. He also had a splinter fracture on his upper fibula and a broken big toe. It sure would be nice to have video so that we could figure out what happened. The back tire washed out as he was making a left onto the street from the alley is all we know. The bike's damages amounted to $4700. Check out the pics. There are x-rays before surgery and after.

[Skinner]

Please understand that if the sight glass opening was typical then I would agree that JB Weld would not be a good choice. A 18mm (or in this case, 21mm) hole into the reservoir means a JB Weld "plug" could blow out, as previously suggested. However, the sight glass opening on the Katana is different. It's larger in diameter for one thing, which means typical glass replacements from EBay won't work. And it's not just a large hole opening into the reservoir either - see the attached pic from when I removed the original sight glass. It has a solid aluminum backing with 2 small holes to allow the brake fluid through to be seen in the sight glass. And the interior of the opening has a groove where a rubber o-ring once sat (difficult to see in the pic), which will lock the cured JB Weld in place. So you can see that I'm not just filling a big hole with a plug that could slip out.

In hindsight I should have been more clear about the nature of the repair and I did intend to suggest something unsafe. My solution for this particular MC will be at least as strong - probably much stronger - than the original sight glass. The only drawback is that I cannot readily see the brake fluid level.

[posplayr]

Please understand that if the sight glass opening was typical then I would agree that JB Weld would not be a good choice. A 18mm (or in this case, 21mm) hole into the reservoir means a JB Weld "plug" could blow out, as previously suggested. However, the sight glass opening on the Katana is different. It's larger in diameter for one thing, which means typical glass replacements from EBay won't work. And it's not just a large hole opening into the reservoir either - see the attached pic from when I removed the original sight glass. It has a solid aluminum backing with 2 small holes to allow the brake fluid through to be seen in the sight glass. And the interior of the opening has a groove where a rubber o-ring once sat (difficult to see in the pic), which will lock the cured JB Weld in place. So you can see that I'm not just filling a big hole with a plug that could slip out.
[ATTACH=CONFIG]55015[/ATTACH]
In hindsight I should have been more clear about the nature of the repair and I did intend to suggest something unsafe. My solution for this particular MC will be at least as strong - probably much stronger - than the original sight glass. The only drawback is that I cannot readily see the brake fluid level.

You know the saying, "Never trust anything a PO did"? Well, this thread is a clear demonstration of that. I just hope any potential new owner figures it out before the MC blows out. Obviously, I would not want it to fail on you either, but you seem so cavalier about this that it is hard to be too concerned.

[Skinner]

Posplayr, I don't think I'm being "cavalier", I'm just confident in this solution. I fail to see how using epoxy to secure a piece of Lexan or a watch crystal into an opening such as this is any stronger than filling the opening with JB Weld. I'm more than willing to admit or correct a mistake if I'm wrong, but in this case I just don't see it. Is there something about JB Weld and brake fluid that I'm not aware of? What is the rationale for thinking it will blow out? Because of the groove around the inside of the opening the cured JB Weld is mechanically locked into place. It's not coming out unless I take a drill to it.

[Nessism]

The issues as I seem them are 1) JB Weld is an adhesive, not a filler, and needs to be kept thin in order to function as intended, and 2) how do you know JB Weld won't be degraded by brake fluid?

Don't lose focus on the fact that we are talking a critical system on the bike that affects safety too.

[Steve]

Maybe somebody else will see it in time.

Not sure I understand what you mean...

I think he was saying that if someone else has the same problem, that they might see his suggestion and act on it, before they remove the sight glass and fill the hole with JB weld.

That is exactly what I was thinking. No drama intended, but somewhere down the line, someone else is going to read this thread and see at least two ways of doing the job.

I fail to see how using epoxy to secure a piece of Lexan or a watch crystal into an opening such as this is any stronger than filling the opening with JB Weld.

I'm not saying it's any stronger, just that it retains the ability to monitor the fluid level and color.

I know that JB is rather resistant to most chemicals, I don't know whether brake fluid affects it or not, but you certainly can NOT see through it.

As far as mechanical integrity is concerned, the groove for the o-ring will certainly enhance its ability to stay in place. I don't know how it would "blow out", as there is no pressure generated in the reservoir. The only reason I could see it failing would be if it is affected negatively by brake fluid.

.